Eco-friendly Masonry Units A Review Article on Suitability of Masonry Units Manufactured with Waste Products in Construction

The huge volume waste generated, its disposal and the excessive dependence on exhaustible natural resources are two major problems faced by mankind. The materials used in the construction industry are derived from naturally available resources such as limestone, river sand, stone (rock), clay etc. The exponential increase in the construction activities in India over the last few decades has led to over exploitation of these natural resources. Due to the large population of the country, large volumes of domestic and industrial waste are generated, which poses a problem of disposal due to shortage of land. Masonry units constitute a large proportion of the volume of construction materials. In this review article the above mentioned two problems are addressed by utilizing waste materials to replace conventional construction materials in masonry units. For this, studies carried are out by various researchers on the properties of masonry units incorporated with waste is reviewed and from the data it can be inferred that these “Eco-friendly” masonry units can replace the conventional ones, thereby reducing the volume of waste to be disposed of and the demand of natural resources required in construction industry. Keyword masonry units; waste; compressive strength; water absorption.

Concrete (AAC) blocks manufactured by replacing sand and lime with sugar sediment waste and found that the compressive strength of the blocks improved considerably. Lixiong Cai et al. [7] studied the performance of AAC blocks by using iron tailings as a substitute for silicon sand and found that the increase in the percentage of iron tailings had a negative effect on the compressive strength of AAC blocks. Yiquan liu et al. [8] prepared AAC blocks by replacing aluminum powder with aluminum dust and found that aluminum dust can be considered as an alternative foaming agent for AAC production. Eric Ababio Ohemeng et al. [9] studied the performance of rubberized concrete blocks manufactured by replacing sand with Ground Vehicular Tyre (GVT) rubber and found reduction in density and compressive strength with increase in rubber content. Indara Soto Izquierdo et al. [10] studied the performance of hollow concrete block reinforced with sisal fiber and found that the replacement of sisal fibre reduces the compressive strength of the blocks marginally. Pierre Matar et al. [11] studied the properties of concrete blocks manufactured using recycled aggregates and finally it was concluded that using recycled aggregates without natural aggregates in manufacture of blocks is not economical.

II. DIFFERENT WASTE PRODUCTS USED IN MASONRY UNITS A. Properties of Clay Based Masonry Units
In this section the properties of clay masonry units by replacing clay with different waste products, as determined experimentally by different researchers, have been tabulated in Table I for comparison. It is seen that the clay units with 10-30% replacement of clay by paper industry waste showed a reduction of about 60-88% in compressive strength and increase in water absorption by 30-60% [1]. Further, clay units with 10-30% replacement by a mixture of limestone powder wastes and wood wastes showed a reduction in compressive strength and density by 33.33-71% and 9.5-19.6% respectively and increase in water absorption by 10.79-35.41% [2]. Substitution of clay by 15% SBA in the production of burnt clay bricks reduced the compressive strength and density by 50% and 14% respectively and increased the water absorption by 23.86% [3]. Substitution of clay by 15% RHA in the production of burnt clay bricks reduced the compressive strength and density by 41% and 7% respectively and increased the water absorption by 20.5% [3]. Brick specimens incorporating SBA showed more reduction in density compared to that of bricks incorporating RHA which may be attributed to the lower unit weight of SBA (274.6kg/m³) as compared to RHA (587.5kg/m³).

B. Properties of Cement Based Masonry Units
In this section cement bricks manufactured by adding different types of waste products have been compared. Researchers have tested the bricks for various mechanical properties such as compressive strength and physical properties such as water absorption (Table II). In [4] bricks were cast using self-compacting mixtures of bottom ash, fly ash and cement with varying ratios of BA and FA from 1:1 to 1:1.25. It is found that the maximum compressive strength was 17.36 MPa for FA: BA ratio 1:1.25 which was 30.8% greater than conventional cement bricks. The alkali activated cement bricks produced using RCBW, CW and GW mixed with different proportions of OPC and activating solution containing NaOH and water glass, the authors of [5] observed an increase in compressive strength and the maximum compressive strength of RCBW blocks with 20% OPC was 102 MPa which was 88% greater than that of conventional cement bricks. The highest compressive strength of CW blocks with 30% OPC was 33 MPa which was 63.6% greater than that of conventional cement bricks and the maximum compressive strength of blocks of GW (100%) was 57 MPa which was again greater than conventional value by 80% [5].

C. Properties of Cement Based Masonry Units
In this section the properties determined by different researcher of AAC blocks manufactured by using different industrial wastes have been presented in Table III. Properties such as compressive strength, density and water absorption of AAC blocks have been compared. The AAC blocks were manufactured by replacing 30% sand weight and 7.5% lime weight with 30% sugar sediment waste. From the test results, the researchers found that maximum compressive strength was 5.9 MPa for 30% sugar sediment. The density was found to be 0.54 g/cm³ and water absorption was found to be 40% for 30% sugar sediment [6]. The AAC blocks were also manufactured by using iron tailings to replace silicon sand. The authors used eleven mix proportions of varying percentage of iron tailings. From the results they found that replacing silicon sand by iron tailings did not much affect the density. The compressive strength was found to decrease on addition of iron tailings and the compressive strength was found to vary between 3.15 MPa to 2.5 MPa for iron tailings varying from between 0-50%. Thus researchers found that increased proportions of iron tailings had a negative effect on compressive strength of AAC blocks [7]. The AAC blocks manufactured by replacing the Al powder with Al dust as in [8] were tested for various properties. From their study the authors found that the Al dust incorporated blocks possess density of around 0.8 g/cm³ and compressive strength of about 2.5 MPa.

D. Properties of Cement Based Masonry Units
In this section the properties of various concrete blocks incorporated with different wastes are tabulated (Table IV). Researchers observed the variation in properties after adding different kind of wastes to the conventional concrete blocks. The authors of [9] conducted tests on blocks manufactured by replacing sand volume with rubber content in the range of 0-60% and w/c ratio between 0.20-0.35. All the mixtures where proportioned with fixed aggregate/cement ratio of 5.25. Tests were conducted on manufactured blocks to analyse the density and compressive strength. The compressive strength was found to be maximum for w/c ratio 0.35 and rubber content of 10%. The compressive strength obtained was 44.21 MPa and density was 2.184g/cm³. Further increase in rubber content resulted in reduction of compressive strength and density. For hollow concrete blocks reinforced with 1% sisal fibre reduction in compressive strength was observed [10]. Compressive strength decreased nearly by 26% compared to blocks in plain concrete, whereas water absorption and number of voids where found to increase. The compressive strength for blocks reinforced with sisal fibres was 13.43MPa. For concrete blocks manufactured using recycled aggregates with 10% cement content, reduction in compressive strength was observed when compared to blocks manufactured with natural aggregates [11]. The compressive strength for blocks with natural aggregates was 18.25 MPa whereas the compressive strength for blocks with 30% recycled aggregates was found to be 9.21 MPa. Reduction of 26.41% in compressive strength was observed.

Water absorption (%) Cement blocks with FA and BA
17.36 -29.2  III. CONCLUSIONS From the literature reviewed on manufacturing clay masonry units by incorporating different waste products as substitutes for clay it can be inferred that presence of waste results in the reduction of compressive strength and an increase in water absorption of the masonry units. This behavior may be attributed to the lower binding properties and higher water absorption capacity of the waste. However, replacing clay with waste resulted in decrease in the density of units due to the lower specific gravity of waste as compared to that of clay. This property is particular beneficial as the dead load of the structure is reduced. As per IS 1077:1992 [12] burnt bricks are categorized from class 35 to 3.5 corresponding to bricks with compressive strength of 35 MPa to 3.5 MPa respectively. From Table 1, it can be seen that although compressive strength of the blocks reduced with increase in replacement of clay by waste, the strength was above 3.5 MPa benchmark. The water absorption shall not be greater than 20% by weight as per IS 1077:1992 [12]. With respect to these criteria it can be concluded that • In clay bricks with paper industry waste, clay can be replaced up to 10% by waste •

Alkali Activated cements with CW
In clay bricks with lime stone powder and wood waste clay can be replaced up to 30% • In clay bricks with SBA and RHA clay can be replaced up to 15% From the experiments conducted by different researchers on manufacturing cement blocks by incorporating fly ash and bottom ash it can be inferred that presence of fly ash and bottom ash in different ratios with different proportions of cement resulted in increase in compressive strength of masonry units. It is observed that increase in the amount of fly ash and cement resulted in increase of compressive strength of mixtures. This may be attributed to the reaction of fly ash with cement during hydration. The chemical reactions increased with increasing amount of fly ash and hence increased the strength [4]. From the results obtained after conducting tests on alkali activated cement blocks by researchers, it can be seen that reusing RCBW, CW and GW resulted in very high compressive strengths of the blocks. The minimum compressive strength for cement blocks in 5 MPa as per IS 2185 (Part 1) 1979 [13] and the results obtained were considerably higher, thus it can be concluded that cement blocks consisting of wastes as in [4] and [5] can be used in construction.
From the results obtained by researchers testing the properties of AAC blocks by incorporating sugar sediment waste as substitute for lime and sand it can be inferred that presence of sugar sediment waste increases the compressive strength when compared to conventional AAC block and a marginal increase in water absorption [6]. From the study done by authors of [7] it was found that, increase in substitution of sand by iron tailing had a negative effect on compressive strength of the blocks. From the results obtained after conducting tests by replacing Al powder with Al dust the researchers found that this had a negligible effect on compressive strength and therefore Al dust can be considered as an alternative foaming agent for Al powder [8]. As per IS 2185 (Part 3) [14] the compressive strength of AAC block should be between 1.5 and 6 MPa. With respect to this criterion it can be concluded that • Lime and sand can be replaced by sugar sediment up to 30% • Al dust can be used as a foaming agent in AAC blocks as a replacement of Al powder [8] From the literature reviewed on manufacturing concrete blocks incorporating GVT as a substitute for sand, it can be inferred that increase in the proportion of GVT decreased the compressive strength of concrete blocks [9]. However, even with 60% of sand replaced by GVT the compressive strength of blocks was 8.93 MPa for a w/c ratio of 0.35 [9], which is acceptable for concrete blocks as per IS 2185 (Part 1) 1979 [13]. After conducting test on concrete blocks reinforced with sisal fiber, the researchers found that the sisal fiber reduces the compressive strength up to 26%. This can be attributed to the decrease in material density and increase in water absorption due to the presence of fibers. However the compressive strength of the blocks with 1% sisal fiber was 13.43 MPa which is again higher than the minimum as per IS 2185 (Part 1). Sisal fibers were found to increase the tensile strength of the blocks [10]. From the test conducted by the authors of [11], with natural aggregates completely replaced by recycled aggregates, the concrete blocks had higher compressive strength than the ones with only natural aggregates. However, the authors concluded that this would make the blocks uneconomical due to the larger cement demand. The authors recommend replacing natural aggregates only up to 50% by recycled aggregates.
Studies by different researchers clearly indicates that masonry units of different materials incorporated with waste products can be used to replace the conventional masonry units in construction. Thus, there is an immediate need to commercialize such "eco-friendly" units and also to educate the parties involved about the benefits of using such products.